1. Field of the Invention
This invention relates to a process for dehydrating solids in aqueous solids mixtures and recovering said solids for further use. Specifically, it deals with a continuous process for drying aqueous solids using a fluidizing oil and a surfactant in an evaporation process wherein the fluidizing oil and surfactant are recovered and recycled.
2. Discussion of the Prior Art
The recovery of dry solids from aqueous solids mixtures is the object of a large industry. Those solids, whether they be waste solids or valuable solids such as chemical solids for consumption by industries or feed for consumption by humans or animals, present many processing problems, both ecologically and relative to efficiency of production. There have been known many processes for economically producing dry solids and, at the same time, extracting the aqueous phase in a form acceptable for disposal or reuse. In order to facilitate those processes, some methods have used various fluidizing oils so that the slurries formed can be dried at high temperatures and still remain pumpable. Although those processes efficiently produce dry solids and solve the ecological problem, there are still some difficulties associated therewith.
In processes for drying solids by evaporation using fluidizing oils, the solids sometimes tend to form large masses that adhere to the inner walls of the pipeline, vapor chamber and heat exchanger tubes while the oil phase may be circulating with little or no wet solids. There are also instances where circulation is prevented due to the solids settling out and plugging the pipeline or circulating pump. Those wet solids, when not properly dispersed and suspended, may coat the heat exchanger surfaces and then dry as a scale reducing the heat transfer rate in the heat exchanger so that the evaporation rate is reduced markedly and the efficiency of the evaporation is very low. Further, when those wet solids adhere to the walls of the evaporators, pipelines, or holding tanks, they can cause corrosion of those apparatus elements if the solids be of an acidic nature.
There are also cases where a mixture of wet solids and oil in the fluidizing tank or feed tank are not pumped uniformly to the evaporator due to the settling of the solids and the immiscibility of the two phases. That action tends to result in a disproportional amount of either wet solids or oil in the mixture sent to the evaporator and tends to upset the system.
It is apparent, therefore, that there exists a need for a more efficient system for continuously dehydrating solids from aqueous mixtures without the aforementioned problems.